Without limiting the scope of the invention, its background is described in conjunction with automotive electrical systems, as an example.
Conventional automobile microcontrollers, limited as they are to low-power components, are connected to the rest of an automobile's electrical system through intermediary relays and high-power devices. For example, an automobile microcontroller may be connected to an indicator light, cornering lamp or even a headlamp through a relatively high-power lamp driver. A low-power, low-voltage signal line is typically connected to a signal input of a lamp driver. The lamp driver is connected to a 12 volt automobile power supply and the lamp to be driven. The provision of separate integrated circuits divided among power and non-power devices requires more space, separate packaging, an increased number of part-to-part external connections and incrementally greater assembly costs.
Heretofore, in this field, high-power electronic components had to be fabricated on integrated circuit chips separate from IC chips for low-power, logic components. Conventionally, high-power transistors had different processing requirements that were not easily integrable with low-power logic devices, such as 5-volt insulated-gate field transistors. On the one hand, certain voltage regulator and power devices mandate that power transistors directly exposed to the usual 12-volt conventional automobile electrical system be capable of withstanding transients that may be as high as 60 volts. On the other hand, the implantation, isolation and doping characteristics of these devices made their cofabrication with smaller, process-labile devices difficult. For example, submicron devices are usually sited within tanks having relatively high dopant concentrations. The implantation energies and concentrations of these tanks are generally incompatible with the corresponding implantation energies and dopant concentrations for high-voltage, high-power devices. It is, however, desirable for automobile system microcontrollers to be monolithic, i.e., fabricated on the surface of one semiconductor chip, rather than have one chip for voltage regulation and other high-power applications and another chip for the performance of logic and the like.